Rheumatoid arthritis (RA) is a disorder characterized by defective immunoregulation. Hypergammaglobulinemia, circulating immune complexes (IC), and autoantibodies such as rheumatoid factor (RF) are common serum abnormalities. To assess IC-mediated feedback suppression in RA, we evaluated the ability of a suppressive B cell factor (SBF) generated by culturing heat-aggregated IgG (HAIgG) with peripheral blood mononuclear leukocytes (PBL) from patients with RA and normal controls to suppress the pokeweed mitogen (PWM)-induced RF plaque-forming cell (PFC) response of normal PBL. RA patients generated less SBF than age-matched controls. Background suppression (supernatants obtained from PBL cultured without HAIgG) was similar in the RA patients and age-matched controls. To determine the effects of nonsteroidal antiinflammatory drug (NSAID) therapy on suppression, RA patients and age-matched controls were studied before and after NSAID therapy. NSAID therapy significantly reduced background suppression in RA patients who were not on immunosuppressive drugs and in age-matched controls, but there was no effect on SBF in RA patients or controls. There was a small increase in background suppression when NSAID were administered to RA patients on immunosuppressives, suggesting an ameliorative effect of NSAID in this group of patients, which tended to increase their level of suppression when compared with RA patients only on NSAID. Spontaneous RF-PFC were measured in normal controls and RA patients and were compared with suppressor activity. There were increased numbers of spontaneous RF-PFC in RA patients. Total suppressor activity was greatest in young adult controls, who also had the least RF-PFC. The percentage of suppression correlated inversely with the number of RF-PFC in patients and controls. Additionally, disease activity in RA as measured by total joint count and erythrocyte sedimentation rate (ESR) was shown to correlate inversely with total suppressor activity. We conclude that the PBL from patients with RA produce decreased SBF after HAIgG stimulation and that loss of suppression is also associated with aging. This study suggests a defect in IC-stimulated B cell suppressor activity in RA leading to decreased ability to suppress antibody and further IC formation. The combination of increased RF-PFC and decreased SBF suggests that there is defective B cell autoregulation in RA, which may be involved in the pathogenesis and chronicity of this disease.